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Philip Kim Department of Physics, Columbia University

Electron Interaction with Spin and Pseudospin in Graphene

Electrons confined in two dimensions (2D) can exhibit strongly correlated states. The quantum Hall ferromagnetism (QHFM) and fractional quantum Hall effect (FQHE) in 2-dimensional electron gas with multiple internal degrees of freedom provides a model system to study the interplay between spontaneous symmetry breaking and emergent topological order. In graphene, the structure of the honeycomb lattice endows the electron wave functions with an additional quantum number, termed valley isospin, which, combined with the usual electron spin, yields four-fold degenerate Landau levels (LLs). This additional symmetry modifies the QHFM and FQHE with intriguing interplay between two different spin flavors. Interacting systems with internal symmetries will tend to break those symmetries in order to lower their energy. Here, the strong Coulomb interactions and approximate spin-pseudo spin symmetry are predicted to lead to a variety of integer quantum Hall ferromagnetic and fractional quantum Hall states and the quantum phase transition between them. We will discuss several recent experimental evidences to demonstrate the role of the electron interaction in single and bilayer graphene under magnetic fields.


C.J. van der Beek - X 01 69 33 40 90 (

Y. Sidis - LLB 01 69 08 96 85 (

V. Brouet – LPS (coordinatrice) 01 69 15 53 34 (

F. Rullier Albenque - SPEC 01 69 08 75 48 (